This invention relates to a multistage in-line rotary pump comprising a closed pump body, a base element provided with suction and delivery connectors and a head element, the pump body being surrounded by a cylindrical jacket or casing spaced from it to form an annular return volume and said casing being braced between the base and head elements by means of stay bolts and flat joints.
So that the in-line principle may be embodied in such pumps with suction and delivery connectors situated on the same axis, the flow conveyed has to be led back to the suction side, situated in the base element from the delivery side of the pump body situated in the head element. This occurs within an annular volume between the pump body and the casing enclosing it. Since the casing and the base and head elements form the pressure-tight delimitation between the fluid and the environment, these components must be sealed with respect one to another. This may be accomplished either by shaped seals or packing boxes, which is however onerous and costly.
A pump of this nature becomes substantially simpler and cheaper if the base element, the casing and the head element are sealed with respect to each other by flat joints. One disadvantage of this structural solution however is that the joints will be located in areas of high areal compression. A torque acting against the direction of rotation of the motor, which tends to twist the parts which are to be sealed with respect to each other is engendered when the motor is turned on or off. If relative displacements occur between the sealed parts during switching the risk arises that the joints may be cut up because of the sharp edges of the casing and that the pump will break down after only a brief period of operation. To prevent damage of this kind, the components in question are commonly tightened against each other more powerfully than is actually required for sealing purposes.
So that the joints are not cut up, that is to say to reduce areal compression, it had already been proposed that the extremities of the jacket or casing should be flanged over or made larger as regards the effective compression area by insertion of a ring, the ring normally being welded to the casing. The flanging-over operation does not resolve the problem in the case of thin-gauge casings because the flanged area may be pushed up by the comparatively great forces, so that this measure will not prevent excessive compression of the joint. The insertion of a ring to enlarge the contact surface furthermore has the disadvantage that a corrosion-promoting interstice will normally be formed.